From the Intricate Mind of our Resident “Mad Scientist”….

by Pavan Kaushik – In the Dark, Dingy, Disordered Dungeon, a Deranged Deductionist Dabbles a Diptera to Dissect a Dialectic of Dendritic Decisions. I work in a slightly messy room, trying to understand decision making in flies. In the process, I am necessitated to build custom experimental apparatus from the things around (Jugaad is what they call it here in India). And a quintessential tool in this process is a vice. A clamp which holds the object of interest. The handle which is used to tighten or loosen the grip was broken and that caused a severe annoyance. To fix it, one has to weld the broken part. Since, I neither have the tools or the skills to weld, I thought of using solder. Naively, I thought solder as a poor man’s welder. I took my solder and flamethrower. Suited up with a labcoat and goggles. Got a fire extinguisher handy, just in case and blazed away at the joint to be soldered. Still blazing…

Still blazing…

Still blazing…

Finally, the solder melts. The solder is on the handle joint of the metal vice and large metal blocks are fantastic heat sinks. But heat sinks prevent things from heating up and here, prevent the solder from melting. But given enough heat, time and patience, a blob of solder on a heat sink will melt. But OOPS. The molten blob rolls and drips to the floor with a splash. As I know it is futile to cry of over spilt solder, I pick up the hot, frozen splash of labour.

I look at it in awe, as it looks like a snapshot of the splashing process, except it is a physical entity and not a photograph. To understand what happened, we need to know a little bit of what solder is. Solder is an alloy of tin and lead (lead free is hard to come by) and is made such that it has a very low melting point. This makes soldering and desoldering a snappy process as it can be melted and frozen rapidly. So, when the bead of solder was dropping to the floor, the air starts to cools it down, an oxide layer forms on the exposed surface and then it makes a touchdown to the floor. In that brief moment of touchdown, multiple phenomenon happen rapidly. The solder is almost about to freeze, making it very viscous and when it makes contact. It splashes like any other liquid, except, this contact with a relatively cool surface and the splash causing a large increase in its surface area results in the freezing of solder to solid in a brief instant. This freezes the solder mid splash creating a snapshot of the splash, a splash-shot.

One can see the fingers, the same crown effect that happens in water splashes. There are ridges on the fingers, similar to the layers on the solidifying lava. But also, one can see cells. The cells look awfully similar to Benard cells. Rayleigh–Bénard convection cells are the patterns you might’ve seen if you have spent some time cooking dishes like upma.

Briefly, these are the convective cells that happen when a plane horizontal fluid has a temperature gradient in the vertical axis. Because of buoyancy, the hotter, less dense liquid rises and cooler, denser liquid sinks. These cycles are repeated periodically in space and have a characteristic length. Since benard cells can easily be done in the lab in multiple ways and has theoretical tractability, it has been used as a model system to study convection. These phenomenon are also responsible for the structure of the Sun’s photosphere. This is why it is a great simplified model system which gives insights on large, complex, intractable but critical systems like the Sun, which clearly cannot be experimentally manipulated. These fantastic toy models improve our understanding of the universe by a great deal. Thus (drumrolls please):